The Measurement of Arterial Pressure in Man. 511 



The measurements of systolic pressure thus show an increase in the calf 

 reading brought about by raising the pressure in the thigh armlet to 

 40-50 mm. Hg. 



We find that the increase in the force of the pulse beat in the artery distal 

 to an armlet coincident with the rise of armlet pressure from to 50 mm. is 

 correlated with the appearance of certain sounds audible with a stethoscope 

 (Bowies' tambour form was used) placed at the elbow. 



An armlet is placed on the upper arm and the stethoscope laid without 

 pressure at the bend of the elbow ; on raising the pressure in the armlet 

 above systolic pressure and then lowering it gradually, clear sounds became 

 audible, gradually getting louder ; these are followed first by murmurs and 

 then by loud clear sounds. At a certain level, which is taken as the index 

 of the diastolic pressure, the loud clear sounds suffer a sudden diminution in 

 volume and tone, to be succeeded by dull sounds ; these may be audible 

 much below diastolic pressure, e.g. 28-35 mm. or so. 



These dull sounds, we believe, are due to the sudden tension of the artery 

 and its branches produced by the impact of the systolic wave. This sets the 

 mass of tissue enclosed in the armlet into vibration, the vibrations becoming 

 audible to the ear as sounds. In the case noted previously these dull sounds 

 appeared when the pressure in the armlet enclosing the upper arm reached 

 35-40 mm. Hg. At precisely the same level the force of the pulse beat 

 could be felt increased while palpating with the fingers the radial artery at 

 the wrist. When the subject took violent exercise the dull sounds became 

 audible when the pressure in the armlet reached 10 mm. Hg, and increased 

 in loudness with successive increments of this pressure. 



In aortic disease, where the pulse-pressure range is high and the artery 

 with each systole suffers considerable distension, the sounds are audible at 

 the bend of the elbow under ordinary conditions. These sounds are at once 

 increased in volume when the pressure in the armlet is raised 5-10 mm. ; at 

 precisely the same levels of external pressure the finger feels the pulse grow 

 stronger, and the sphygmographic tracing confirms the sensory impressions 

 from the fingers. 



Therefore we conclude that a sound is given forth dependent on the 

 pulse-pressure range of the blood stream which enters the armlet. If 

 that range is high, e.g. in aortic disease, the systolic wave is big enough to cause 

 the sounds to be produced under ordinary conditions. If the pressure within 

 the armlet is raised 5—10-20-30-40 the systolic wave is reinforced by the 



resistance to compression by the bag of the pocket sphygmometer. Further, it is difficult to 

 suppose that the arteries in either leg should offer the same local resistance to compression 

 and a resistance wholly different to that of arteries in other parts of the body. 



